0-30 Vdc Stabilized Power Supply

[audioguru2]

I am Iranian. And I've closed the project. Much higher.thanks you
You can just see you here
www.dehnokit.blogfa.com

You built the original project that used old parts that were overloaded so it is not reliable.
This improved version uses modern parts operating within their maximum limits.

 

[Tompa1]

Hi

week ago i finished this PSU ( with latest part list). I have one problem, with current regulation; ammeter shows me some current ( when i connect something) but i cant regulate it ( current), LED light up when i turn potentiometer to the max, then voltage drops. Voltage regulation works fine... Maybe i wrong connected ammeter ( I attached picture how i connect it).

sry for my english...

TY

View attachment 41673

 

[audioguru2]

Hi Tompa,
Since your current meter is in series with the load then its resistance reduces voltage regulation at the load. It will be better to use a voltmeter to measure the voltage across R7 which shows the amount of output current without reducing the voltage regulation.

When the current control is turned to minimum then the current regulation begins when the current is a few mA.
When the current control is turned to maximum then the current regulation begins when the current is 3.0A.

The current regulator reduces the output voltage until the load current is what is set by the current control. When regulating the current then the LED should light to warn you that the output voltage is being reduced.

 

[Guest]

Been lurking around here for a while, I built this power supply over the course of a few years and it's served me well in it's half completed state (need to build the DMM project here to finish it).

However, for some reason, at times, Q1 will turn on (this should turn on only on powerdown?) and start cooking U2 (output drops to 0.15v at any setting). If left off for a day, it will work properly again until it randomly occurs again.

Pin 6 of U2 measures 42.9v
D5 measures 0.3v instead of -6.1v
D7 measures ~0.2v instead of -5.74v
The electrolytic caps C1, C2, C3 and C7 are not damaged and show the proper capacitance.

Swapping the TLE2141s around confirms that the chips are not damaged as it works properly for a while.

Could having a 10k pot for RV1 instead of 5k be the cause?
I'm otherwise completely stumped as I've measured all parts of the -5.6v negative supply and they all check out fine.

EDIT: Added diagram of PSU version I'm using

View attachment 41697

 

[audioguru2]

Q1 was used when the opamps were TL081 because they had the problem called "Phase Inversion" where the output would suddenly go high when the input became within a few volts of the negative supply (that happens when the power is turned off).

The TLE2141 opamps do not have this problem because they work perfectly when their input is at the same voltage as the negative supply.

The circuit with the TLE2141 opamps was changed so that the negative supply is only -1.3V so that their total supply was never more than their max allowed supply of 44V.
If your negative supply is -5.6V then U2 will have a total supply of about 48V which might blow it up.

Maybe your negative supply is too low because R2 or C2 is bad.

You have pin 4 of U3 connected to the power input ground instead of to the negative supply.
Its output must be able to swing at least -0.8V (that is why the new negative supply is -1.3V) so tha D9 can reduce the input of U2 to 0V when the output is shorted.

 

[Guest]

Thanks for the advice audioguru, it's much appreciated.

Looks like I'm going to have to remove a few components and correct a mistake on the PCB. (U3 gets it's "negative" supply from the 0v rail which doesn't seem right.)

 

[Guest]

Finally, fixed the problems with my PSU and updated it to the latest (March 2009?) version.
Turns out that the trace from the AC supply to R2 was intermittent, causing the negative supply to fail.
The output was very low due to the trace out of the base of Q2 being broken.
Next, a digital multimeter to finish off the PSU.

Thanks again audioguru!

 

[Alf_Melmok]

Hi All!

What do you think about this version of the scheme?
But i have only 19,8VAC transformer. Can i use this scheme having replaced U4 on 7818, D13 on 2,4v zener? Will it work? Is this scheme reliable?

(sorry for my english)

View attachment 41711

 

[audioguru2]

What do you think about this version of the scheme?
But i have only 19,8VAC transformer. Can i use this scheme having replaced U4 on 7818, D13 on 2,4v zener? Will it work? Is this scheme reliable?

Since your voltages are very low, many resistor values will need to be re-calculated.
You do not need to use U4 and D13 since without them the unregulated positive supply is only +26V which is fine for a TL071 or TL081 opamp.

With U4 and D13 the maximum output voltage will be only about +14.4V. Without U4 and D13 the maximum output voltage will be about +20V.

If U5 is a -5V regulator then it will not work (it is not needed anyway) since its input voltage is too low.

 

[Alf_Melmok]

Since your voltages are very low, many resistor values will need to be re-calculated.

Can you help me?

You do not need to use U4 and D13 since without them the unregulated positive supply is only +26V which is fine for a TL071 or TL081 opamp.

I want to limit the input voltage. If the line voltage change. So that the output has always been a 20V.

With U4 and D13 the maximum output voltage will be only about +14.4V. Without U4 and D13 the maximum output voltage will be about +20V.

Just in this scheme, the output voltage 30VDC (U4+D13=30,2V). I decided if I'm have 20V, then i  need replace the U4 and D13 (18+2,4=20,4V). I was wrong? The output voltage of 20V was enough for me.

If U5 is a -5V regulator then it will not work (it is not needed anyway) since its input voltage is too low.

It also surprised me. I think D7 not needed. Am I right?
Or, maybe, you advise me another way in my situation. I read this and some similar forum almost 2 weeks and dont know what to do. Thank you anyway.

 

[audioguru2]

Can you help me?

Too much trouble. Use the proper 28VAC or 30VAC transformer and the proper opamps.

I want to limit the input voltage. If the line voltage change. So that the output has always been a 20V.

I don't know why your input voltage changes, mine does not change.
A TIP3055 at 3A has a maximum base-emitter voltage loss of 1.7V.
A BD139 at 110mA has a maximum base-emitter voltage loss of 0.8V.
The 1k series base resistor R15 feeding the BD139 has a maximum voltage loss of 1.5V.
Opamp U2 has a maximum voltage loss of about 3.3V and you are powering it with only +20.4V.
Then the maximum output voltage can be as low as +13.1V when calculated properly.

I decided if I'm have 20V, then i  need replace the U4 and D13 (18+2,4=20,4V). I was wrong? The output voltage of 20V was enough for me.

You forgot to see the voltage losses on the datasheets.
The corrected and improved circuit here has an output of +30V at 3A when its unregulated positive supply is +37.6V from a rectified 28VAC transformer.

I decided if I'm have 20V, then i  need replace the U4 and D13 (18+2,4=20,4V). I was wrong?

Yes you are wrong.

I think D7 not needed. Am I right?

No.
D7 is a negative 5.6V regulator. It was needed in the original project. Your additional 5V regulator U5 is not needed.

 

[Alf_Melmok]

You are right, i forgot about  the voltage losses.
In my country mains voltage change from 200 to 240 very often (In rare cases, even is worse (phase is not uniformly loaded)). That's why i want to limit the input voltage.
It's a vicious circle. In my country i can't buy op amp that you recommend. So that i can't use 28VAC transformer. And i can't find 28-30VAC transformer. I can't find another scheme similar PSU. I just want this power supply with 20V transformer.  :'(
Thanks for your help

 

[audioguru2]

Here in Canada my inexpensive mains electricity is 120V. Sometimes it surges very high to 121V and sometimes it drops very low to 119V. It fails maybe every 2 or 3 years for a moment during a thunderstorm.

There are many electronic parts distributors here that have ANYTHING and EVERYTHING at a good price.
If I order a part by phone or online before 8:00PM then it is delivered to me the next morning.

Maybe in your country you should do gardening instead of electronics.

 

[Alf_Melmok]

I envy you. But it's not funny. By our standards in the electrical network there shall be 220V +20 % -20 %. You can calculate how much it turns out (176-264 It's normal ). All of our electronics designed for this.

 

[asdewq]

hey guys i need some help

i've built this psu project from the first schematic (the original) with the tl081 and everything and it didn't burn up immediately after being switched on as suggested by some

i tried testing the circuit and the current limitation/regulation works fine but voltage regulation does not and im wondering if anyone has had the same problem or if someone has a suggestion as to how to fix this problem

this is a great project and i need this psu for some other projects  and i've spent quite a lot of money on parts (electronics parts are still a bit expensive where i live) and i would hate it this build was a waste of time and money

please help and thank you in advance

 

[asdewq]

after about two more hours of tinkering with the psu i finally got some kind of reaction on the output of the psu but now i can only get either 0V or 31V nothing in between

any suggestions?

 

[audioguru2]

The input to the output amplifier is 0V to +11.2V from the voltage adjust pot.

The output amplifier is simply opamp U2 with the driver transistor and output transistor as emitter-followers boosting the output current. The output amplifier has R11 (27k) and R12 (56k) for over-all negative feedback which sets the gain too high at (56k/27k) + 1= 3.074. Then the output should be able to go from 0V to (11.2V x 3.074=) 34.4V if the unregulated DC voltage is high enough.

Maybe you have the pins on the driver transistor or output transistor mixed up so that they are on-off switches instead of emitter-followers.

 

[asdewq]

Solved it. I accidentaly put the wrong transistor in the wrong place.

Just one more thing. I tested one circuit (I built two) by shorting the output to see the max current rating and it put out almost 5 amps. Those 5 amps burned through the rectifier diodes but everything else was fine. Did you get 5 amps as max current on the output?

 

[audioguru2]

Yes, the original project was missing calibration trimpots to reduce the maximum output voltage to 30.0V and the maximum output current to 3.0A.
The modified circuit has the calibration trimpots added and uses a high current rectifier bridge module that can be bolted to a heatsink.

 

[asdewq]

Would you mind posting a link to the modified circuit?